A nitride semiconductor represented by gallium nitride has large band gap, and interband transition is a direct transition. Therefore, the nitride semiconductor is a useful material for light emitting devices at relatively short wavelength side such as ultraviolet, blue or green light emitting diodes and semiconductor lasers, and semiconductor devices such as electronic devices. Light-emitting devices are generally produced by growing a Group 13 metal nitride crystal in the periodic table on a substrate. And it is known that when Group 13 metal nitride crystals in the periodic table are grown on different kinds of substrates, light-emitting devices having a good efficiency cannot be provided on account of the generation of stacking faults (see Non-patent Documents 1-4), while high-performance light-emitting devices can be provided when Group III metal nitride crystals in the periodic table are homoepitaxially grown on an independent substrate of periodic table Group 13 metal nitride having no stacking faults (see Non-patent Document 3). Hence, in order to provide high-performance light-emitting devices, there exists a need to provide periodic table Group 13 metal nitride crystals which are free of crystal faults such as stacking faults.
One typical method of producing a periodic table Group 13 metal nitride substrate entails the following. A crystal is homoepitaxially grown on a periodic table Group 13 metal nitride seed having a polar plane such as the (0001) plane as a principal plane, following which the crystal is machined so that the desired plane emerges, thereby giving a periodic table Group 13 metal nitride substrate having a specific plane as the principal plane. For example, after GaN has been homoepitaxially grown on the (0001) plane of a GaN crystal seed, by polishing or cutting the crystal so that the (10-10) plane emerges, it is possible to obtain a GaN semiconductor substrate in which the principal plane is the nonpolar (10-10) plane. GaN semiconductor substrates obtained by such a method have been confirmed to have few stacking faults (see Non-Patent Document 2 and Non-Patent Document 5). However, in methods of growing a crystal on a seed in which the principal plane is a polar plane, one challenge has been the difficulty of providing a large-size semiconductor substrate in which the principal plane is a plane other than such polar planes.
Compared with the foregoing method that makes use of a polar plane, very little literature exists on methods of homoepitaxially growing a crystal using a periodic table Group 13 metal nitride seed in which the principal plane is not a polar plane.
For example, Patent Document 1 describes the approach of fitting together nitride semiconductor bars whose principal plane is the M plane by means of raised and recessed features provided on the C plane serving as the side wall, and growing a nitride semiconductor layer on the resulting array of nitride semiconductor bars.
Patent Document 2 describes a method of manufacturing a high-grade nitride semiconductor crystal having a non-polar plane of large surface area, which method entails growing the crystal in the +C-axis direction of a seed crystal.
In addition, Patent Document 3 describes an example where a GaN thin-film in which (10-10) plane serves as the principal plane was grown on (10-10) plane of a sapphire substrate, following which a 1.5 mm thick GaN crystal was grown by a liquid phase process. The same document reports that the number of stacking faults in GaN crystals wherein the (10-10) plane served as the principal plane that were grown was 104 cm−1.
In addition, Patent Document 4 describes growing a 3 mm-thick GaN crystal by hydride vapor-phase epitaxy on a plurality of gallium nitride (GaN) crystal fragments in which the principal plane is a plane other than {0001} planes. Patent Document 5 describes growing a GaN crystal by hydride vapor-phase epitaxy on an underlying substrate having a principal plane with a misorientation angle relative to {1-100} planes of at least 4.1° and not more than 47.8°.
Patent Document 1: Japanese Patent Application Laid-open No. 2006-315947
Patent Document 2: Japanese Patent Application Laid-open No. 2008-308401
Patent Document 3: Japanese Patent Application Laid-open No. 2010-001209
Patent Document 4: Japanese Patent Application Laid-open No. 2010-013298
Patent Document 5: Japanese Patent Application Laid-open No. 2011-016676
Non-Patent Document 1: Applied Physics Express 1 (2008), 091102
Non-Patent Document 2: Phy. stat. sol. (a) 205, No. 5 (2008), 1056
Non-Patent Document 3: JJAP 46, No. 40 (2007), L960
Non-Patent Document 4: Appl. Phys. Lett. 91 (2007), 191906
Non-Patent Document 5: Applied Physics Express 2 (2009), 021002